Ionic liquids (ILs) are salts in which the cation and anion are poorly coordinated. At least one of the ionic components is organic and one of the ions has a delocalized charge. This prevents the formation of a stable crystal lattice, and results in such materials existing as liquids, often at room temperature, and at least, by definition, at less than 100° C. For example, sodium chloride, a typical ionic salt, has a melting point of about 800° C., whereas the ionic liquid N-methylimidazolium chloride has a melting point of about 75° C.
Ionic liquids typically comprise an organic cation, such as a substituted ammonium or a nitrogen-containing heterocycle, such as a substituted imidazolium, coupled with an inorganic anion. However, species have also been described wherein the cation and anion are organic. When the ionic liquid comprises at least one polymerizable group, such ionic liquid is a polymerizable ionic liquid (“PIL”).